Stable Silicon Research Articles

Single-electron transport through stabilised silicon nanocrystals.

We have fabricated organically capped stable luminescent silicon nanocrystals with narrow size distribution by a novel, high yield and easy to implement technique. We demonstrate transport measurements of individual silicon nanocrystals by scanning tunnelling microscopy at a low temperature in a double-barrier tunnel junction arrangement in which we observed pronounced single electron tunnelling effects. The tunnelling spectroscopy of these nanocrystals with different diameters reveals quantum confinement induced bandgap modifications. Furthermore, from the features in the tunnelling spectra, we differentiate several energy contributions arising from electronic interactions inside the nanocrystal. By applying a magnetic field, we have detected a variation in the differential conductance profile that we attribute to arising from higher order tunnelling processes. We have also systematically simulated our experimental data with the Orthodox theory, and the results show good agreement with the experiment. The study establishes a correlation between the nanocrystal size and quantum confinement induced band-structure modifications which will pave the way to devise tailored nanocrystals.

Highly photoluminescent and stable silicon nanocrystals functionalized via microwave-assisted hydrosilylation.

Herein, we report a microwave-assisted hydrosilylation (MWH) reaction for the surface passivation of silicon nanocrystals (Si-NCs) with linear alkenes. The MWH reaction requires only 20 minutes and allows us to produce Si-NCs with high photoluminescence quantum yields (PLQYs), reaching 39% with an emission maximum of 860 nm. Furthermore, we investigated the effect of ligand length on the photoluminescence properties of Si-NCs. We tested six alkenes with an even number of carbon atoms (from hexene-1 to hexadecene-1). The highest PLQY combined with a long stability (test period of 6 months) was observed when capping with the shortest ligand, hexene-1. The use of microwave heating turns the hydrosilylation step into a facile and sustainable process. In order to provide insight into the emissive properties of Si-NCs surface oxidation and luminescence decay were investigated using Fourier-transform infrared spectroscopy and time-resolved photoluminescence measurements.

Fvs-Si48: a direct bandgap silicon allotrope.

A structurally stable silicon allotrope is predicted by means of first principles calculations. This new structure is composed of a six-membered ring, a five-membered ring and a three-membered ring with the space group PA3[combining macron] and fvs topology, which is named fvs-Si48. The calculations of geometrical, vibrational, and electronic and optical properties reveal that fvs-Si48 has good mechanical stability with a mass density of 1.86 g cm-3. More importantly, it is a semiconductor with a direct band gap of 2.15 eV. From the analysis of its optical properties, there is the possibility of its synthesis in theory. This fvs-Si48 could have a wide range of applications in photo catalysts, optoelectronics, hydrogen storage and aerospace engineering.

Robust Microencapsulated Silicone Oil with a Hybrid Shell for Reducing Propellant Erosion

AbstractA morphologically stable silicon oil microcapsule base polystyrene as shell modified with TiO2 and Si3N4 nanoparticles was synthesized, characterized and applied as an inhibitor for high energy propellant to reduce erosion of gun barrel. The composite microcapsules were obtained by an eco‐friendly method. Embedding heat‐resistant TiO2 and Si3N4 nanoparticles in polystyrene shell enhances the reliability of polymeric shell. The anti‐erosion effect of composite microcapsules for high energy propellant was investigated by using an erosion tester. Results showed that the erosion property of high energy propellant with composite microcapsule was significantly decreased when compared to control sample (without microcapsules). It showed a decrease of 20.6 % in erosion mass when 7 wt.% of composite microcapsules were added to the high energy propellant. Moreover, the anti‐erosion efficiency of composite additives exhibited an increasing trend with the increase of their contents. The pressure and time history confirmed that the composite microcapsules also have ability to adjust the combustion performance of high energy propellants. The developed silicon oil microcapsule shows a potential application for propellant erosion additive.

Structure of the 1d2s Shell from the Data on Single-Nucleon-Transfer Reactions

For the stable silicon isotopes 28Si and 30Si, the energies and occupancies of single-particle states of the 1d2s shell are determined by analyzing the combined data for the nucleon stripping and pickup reactions. From the results of analysis and the available experimental data, the variation of the 1d2s proton-shell structure with increasing neutron number for the silicon isotopes with A = 26–34 is discussed.

Highly Stable Molybdenum Disulfide Protected Silicon Photocathodes for Photoelectrochemical Water Splitting.

Developing materials, interfaces, and devices with improved stability remains one of the key challenges in the field of photoelectrochemical water splitting. As a barrier to corrosion, molybdenum disulfide is a particularly attractive protection layer for photocathodes due to its inherent stability in acid, the low permeability of its basal planes, and the excellent hydrogen evolution reaction (HER) activity the MoS2 edge. Here, we demonstrate a stable silicon photocathode containing a protecting layer consisting of molybdenum disulfide, molybdenum silicide, and silicon oxide which operates continuously for two months. We make comparisons between this system and another molybdenum sulfide-silicon photocathode embodiment, taking both systems to catastrophic failure during photoelectrochemical stability measurements and exploring mechanisms of degradation. X-ray photoelectron spectroscopy and transmission electron microscopy provide key insights into the origins of stability.

Prediction of another semimetallic silicene allotrope with Dirac fermions

Materials with Dirac point are so amazing since the charge carriers are massless and have an effective speed of light. However, among the predicted two-dimensional silicon allotropes with Dirac point, no one has been directly proved by experiment. This fact motivates us to search for other two-dimensional silicon allotropes. As a result, another stable single atomic layer thin silicon allotrope is found with the help of CALYPSO code in this work. This silicene allotrope is composed of eight-membered rings linked by Si–Si bonds with buckling formation. The electronic calculation reveals that it behaves as a nodal line semimetal with the linear energy dispersion relation near the Fermi surface. Notably, the ab initio molecular dynamics simulations display that the original atomic configuration can be remained even at an extremely high temperature of 1000 K. Additionally, hydrogenation could induce a semimetal-semiconductor transition in this silicene allotrope. We hope this work can expand the family of single atomic layer thin silicon allotropes with special applications.

Low-Absorbing and Thermally Stable Industrial Silicon Nitride Films With Very Low Surface Recombination

Amorphous silicon nitride has become the state-of-the-art antireflection coating for silicon solar cells. Optimization of silicon nitride films requires consideration of both the film's optical and electrical properties. It is commonly assumed that silicon-rich silicon nitride films (films with high refractive index) provide better surface passivation, compared to that obtained by films with lower indices. However, silicon-rich films are usually very absorptive in the short (and even medium) wavelength range. Development of low absorption silicon nitride films, that provide good surface passivation, is therefore highly valuable. In this study we compare nine different industrial silicon nitride films, all with similarly low refractive index of 2.09 ± 0.01 measured at 633 nm. We demonstrate that these films exhibit very different electrical, chemical, and optical properties despite their similar refractive index values and correlate these differences with the specific deposition conditions. As a result of this investigation, we have developed industrial thermally stable low-absorbing silicon nitride films that provide excellent surface passivation, with surface saturation current density of 7 fA/cm2 on both n- and p-type wafers. We demonstrate that the developed low absorption films provide surface passivation with equal quality to that obtained by industrial silicon-rich silicon nitride films.

Advances in Phosphasilene Chemistry.

Heavier alkene analogues possess unique electronic properties and reactivity, encouraging multidisciplinary research groups to utilize them in the rational design of novel classes of compounds and materials. Phosphasilenes are heavier imine analogues, containing highly reactive Si=P double bonds. Recent achievements in this field are closely related to the progress in the chemistry of stable low-coordinate silicon compounds. In this Review, we have attempted to summarize in a comprehensive way the available data on the structures, syntheses, electronic and chemical properties of these compounds, with an emphasis on recent achievements.

Continuous electron beam melting technology of silicon powder by prefabricating a molten silicon pool

We successfully achieved the continuous melting of silicon powder in a vacuum electron beam melting system. The characteristic of electron beam melting of silicon powder was revealed by comparing the three different approaches to prefabricate the molten silicon pool. The application of silicon block can be regarded as the most efficient method to prefabricate a stable molten silicon pool. Afterward, the silicon powder was added into the molten silicon pool at different rates by a spiral silicon powder feeding device. Finally, all of the silicon powder was melted completely. Although the P removal efficiency decreases with increasing powder feeding rate during the powder feeding process, an appropriate increase in the powder feeding rate is not only beneficial to improve the melting efficiency of silicon powder but also conductive to the improvement in uniformity of the obtained silicon ingot. Therefore, the powder feeding rate of 10 g/min was the best option in this study. Compared with the melting of silicon block, which has been wildly applied, this continuous powder feeding process can be beneficial to saving smelting time and the total cost.

Evidence for depletion of heavy silicon isotopes at comet 67P/Churyumov-Gerasimenko

Context. The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) was designed to measure the composition of the gas in the coma of comet 67P/Churyumov-Gerasimenko, the target of the European Space Agency's Rosetta mission. In addition to the volatiles, ROSINA measured refractories sputtered off the comet by the interaction of solar wind protons with the surface of the comet. Aims. The origin of different solar system materials is still heavily debated. Isotopic ratios can be used to distinguish between different reservoirs and investigate processes occurring during the formation of the solar system. Methods. ROSINA consisted of two mass spectrometers and a pressure sensor. In the ROSINA Double Focusing Mass Spectrometer (DFMS), the neutral gas of cometary origin was ionized and then deflected in an electric and a magnetic field that separated the ions based on their mass-to-charge ratio. The DFMS had a high mass resolution, dynamic range, and sensitivity that allowed detection of rare species and the known major volatiles. Results. We measured the relative abundance of all three stable silicon isotopes with the ROSINA instrument on board the Rosetta spacecraft. Furthermore, we measured $^{13}$C/$^{12}$C in C$_2$H$_4$, C$_2$H$_5$, and CO. The DFMS in situ measurements indicate that the average silicon isotopic composition shows depletion in the heavy isotopes $^{29}$Si and $^{30}$Si with respect to $^{28}$Si and solar abundances, while $^{13}$C to $^{12}$C is analytically indistinguishable from bulk planetary and meteorite compositions. Although the origin of the deficiency of the heavy silicon isotopes cannot be explained unambiguously, we discuss mechanisms that could have contributed to the measured depletion of the isotopes $^{29}$Si and $^{30}$Si.

Advanced Silicon Anode Enabled By Simple Pouring of Bifunctional Gel Polymer

Electrode structure deterioration and unstable solid-electrolyte-interphase (SEI) are crucial issues hindering the application of silicon anode in high energy lithium-ion batteries.[1-3] Here, we report a simple way to construct a stable silicon anode enabled by pouring branched polyurethane gel that comprise ion-conductive ethylene oxide (EO) soft segment into electrode. This tough gel conformably coated on the electrode components and strongly bonded them together through the chemical bonding and hydrogen bonding, forming a robust electrode. Additionally, it provides mechanical and chemical protection while Li+ transport, behaving as an artificial SEI layer. The harness of bifunctional gel polymer lead to a significant improvement of electrochemical performance with an capacity retention of 90% within 150 cycles and achieve a high areal capacity over 4 mAh/cm2 when micro-sized silicon-based materials was evaluated.

Low-power catalytic gas sensing using highly stable silicon carbide microheaters

A robust silicon carbide (SiC) microheater is used for stable low-power catalytic gas sensing at high operating temperatures, where previously developed low-power polycrystalline silicon (polysilicon) microheaters are unstable. The silicon carbide microheater has low power consumption (20 mW to reach 500 °C) and exhibits an order of magnitude lower resistance drift than the polysilicon microheater after continuously heating at 500 °C for 100 h and during temperature increases up to 650 °C. With the deposition of platinum nanoparticle-loaded boron nitride aerogel, the SiC microheater-based catalytic gas sensor detects propane with excellent long-term stability while exhibiting fast response and recovery time (~1 s). The sensitivity is not affected by humidity, nor during 10% duty cycling, which yields a power consumption of only 2 mW with frequent data collection (every 2 s). With a simple change of heater material from silicon to SiC, the microheater and resulting catalytic gas sensor element show significant performance improvement.

Efficient and Stable Silicon Photocathodes Coated with Vertically Standing Nano-MoS2 Films for Solar Hydrogen Production.

Water splitting in a photoelectrochemical cell, which converts sunlight into hydrogen energy, has recently received intense research. Silicon is suitable as a viable light-harvesting material for constructing such cell; however, there is a need to improve its stability and explore a cheap and efficient cocatalyst. Here we fabricate highly efficient and stable photocathodes by integrating crystalline MoS2 catalyst with ∼2 nm Al2O3 protected n+p-Si. Al2O3 acts as a protective and passivative layer of the Si surface, while the sputtering method using a MoS2 target along with a postannealing leads to a vertically standing, conformal, and crystalline nano-MoS2 layer on Al2O3/n+p-Si photocathode. Efficient (0.4 V vs RHE onset potential and 35.6 mA/cm2 saturated photocurrent measured under 100 mA/cm2 Xe lamp illumination) and stable (above 120 h continuous water splitting) photocathode was obtained, which opens the door for the MoS2 catalyst to be applied in photoelectrochemical hydrogen evolution in a facile and scalable way.

Microstructural degradation of silicon electrodes during lithiation observed via operando X-ray tomographic imaging

Due to their high theoretical capacity compared to that of state-of-the-art graphite-based electrodes, silicon electrodes have gained much research focus for use in the development of next generation lithium-ion batteries. However, a major drawback of silicon as an electrode material is that it suffers from particle fracturing due to huge volume expansion during electrochemical cycling, thus limiting commercialization of such electrodes. Understanding the role of material microstructure in electrode degradation will be instrumental in the design of stable silicon electrodes. Here, we demonstrate the application of synchrotron-based X-ray tomographic microscopy to capture and track microstructural evolution, phase transformation and fracturing within a silicon-based electrode during electrochemical lithiation.

GEOTRACES inter-calibration of the stable silicon isotope composition of dissolved silicic acid in seawater

The first inter-calibration study of the stable silicon isotope composition of dissolved silicic acid in seawater,δ30Si(OH)4, is presented as a contribution to the international GEOTRACES program.

A three-dimensional hierarchical structure of cyclized-PAN/Si/Ni for mechanically stable silicon anodes

We designed a three-dimensional hierarchical structure of cyclized-PAN/Si/Ni by the CVD method for mechanically stable silicon anodes.

Size distribution and visible luminescence of silicon nanoparticles embedded in SiNx thin film: Role of RF power in PECVD

This paper presents, the studies of the influence of (radio frequency) RF power on the size distribution and visible photoluminescence (PL) of SiNx thin film deposited at 300[Formula: see text]C of substrate temperature by plasma enhanced chemical vapor deposition. RF power was varied (5–50[Formula: see text]W), and its aftereffect on the optical properties of thin films was investigated. By increasing the RF power between 5[Formula: see text]W and 25[Formula: see text]W, main PL peak showed a red shift with an increase in PL intensity, which is associated with an increase in the silicon nanocrystals size and density, respectively. Results obtained were confirmed with High-resolution transmission electron microscopy micrographs and from the statistical calculations. By attaining a precise RF power value, stable silicon nitride thin film with suitable optical properties can be achieved for the potential fabrication of optoelectronic devices.

Flexible hybrid coatings with efficient antioxidation properties

Abstract In this work, the feasibility of a transparent sol gel coating on polyamide-polyethylene (PA/PE) substrate with antioxidant properties as active food packaging was investigated. Stable water-based silicon alkoxide formulations, containing lipophilic vitamin E as natural antioxidant, were obtained adding ascorbic acid as catalyst. Comparative blank sols were prepared without antioxidant guest molecules. The sol formulations of tetraethyl orthosilicate and a mixture of alcoxysilane containing organic moieties as phenyl and methyl group were stable and easy to process via dip coating on Polyamide/Polyethylene substrates. Organic functionalities were essential to incorporate the lipophilic guests and to achieve an optimal adhesion on the polymeric substrate. The presence of stable coating was evaluated through Electron Microscopy and Optical Emission Spectroscopy analyses, while the surface roughness and optical absorption were measured by noncontact laser profilometry and by UV/vis spectra. The loaded antioxidant amount was estimated right after the coating deposition by spectroscopic UV measurements in ethanol, as its subsequent release within 14 days. The estimated antioxidant release was 10% and 40% of the loaded amount for the hydrochloric-sol and the ascorbic acid catalysed sol, respectively. The antioxidant efficacy of coatings was evaluated through the Ferric Reducing Antioxidant Power (FRAP) assay showing a significant difference in antioxidant efficacy between the vitamin E containing sols and their blank ones. Those results were confirmed by FRAP analysis even four months after the deposition.

Synthesis and Reactivity of Functionalized Silicon(II) Compounds: Iminosilylene, Phosphinosilylene, Hydrosilylene, and Related Compounds

Abstract Recent decades have witnessed the isolation of a large number of stable silicon(II) compounds along with their applications toward small molecule activation and as versatile ligand systems for transition-metal complexes. The employment of donor stabilization techniques has proven to be an effective mean for stabilization of such silicon(II) systems that is consequently helpful in further reactivity investigations. In this context, an overview of the study of donor-stabilized silicon(II) compounds bearing unique functionalities that have recently been investigated in our research group is presented. By the use of amidinato ligand or N-heterocyclic carbene (NHC), the access to heteroatom-functionalized silicon(II) compounds has been achieved and exploration of further reactivity has led to the isolation of additional novel silicon(II) species. Applications of these silicon(II) compounds as ligands towards transition-metal complexes and in activation of organic and inorganic small molecules are also described.